Shade tree effects in an 8-year-old cocoa agroforestry system: biomass and nutrient diagnosis of Theobroma cacao by vector analysis

Abstract

Farm product diversification, shade provision and low access to fertilizers often result in the purposeful integration of upper canopy trees in cocoa (Theobroma cacao) plantations. Subsequent modification to light and soil conditions presumably affects nutrient availability and cocoa tree nutrition. However, the level of complementarity between species requires investigation to minimize interspecific competition and improve resource availability. We hypothesized beneficial effects of upper canopy trees on cocoa biomass, light regulation, soil fertility and nutrient uptake. We measured cocoa standing biomass and soil nutrient stocks under no shade (monoculture) and under three structurally and functionally distinct shade trees: Albizia zygia (D.C.) Macbr, a nitrogen fixer; Milicia excelsa (Welw.), a native timber species; and Newbouldia laevis (Seem.), a native small stature species. Vector analysis was employed to diagnosis tree nutrition. Cocoa biomass was higher under shade (22.8 for sole cocoa versus 41.1 Mg ha −1 for cocoa under Milicia), and declined along a spatial gradient from the shade tree (P < 0.05). Percent canopy openness differed between the three shade species (P = 0.0136), although light infiltration was within the optimal range for cocoa production under all three species. Soil exchangeable K was increased under Newbouldia, while available P decreased and total N status was unaffected under all shade treatments. Nutrient uptake by cocoa increased under shade (43-80% and 22-45% for N and P, respectively), with K (96-140%) as the most responsive nutrient in these multistrata systems. Addition of low-density shade trees positively affected cocoa biomass close to the shade tree, however proper management of upper stratum trees is required for optimum cocoa productivity and sustainability.

Does Criollo cocoa have the same ecophysiological characteristics than Forastero?

“…The existence of this plantation for so many years in this location seems to confirm that in regions with little access to inorganic fertilizers, litter fall can maintain soil fertility (Isaac et al 2007). Moreover, the reduction in wind speed and evapo-transpiration by trees that provide the shade reduce the water deficit and high temperature of air and soils during the dry season (Beer et al 1998).…”

Ecophysiology of the cacao tree

“…Furthermore, the forest trees used for shade greatly contribute with the formation of soil organic matter, carbon sequestration, nutrient recycling and maintenance of biodiversity (Müller and Gama Rodrigues, 2007;Lobão et al, 2007). Specifically in regions with low access to inorganic fertilizers, the multistrata plantation is used to maintain soil fertility with the subsequent increase in nutrient availability for cacao (Isaac et al, 2007). Forest trees for shading also reduce wind speed and evapotranspiration (Beer et al, 1998), consequently, decrease humidity stresses and extreme air and soil temperatures during the dry season (AnimKwapong, 2003).…”

Seeing the trees: Farmer perceptions of indigenous forest trees within the cultivated cocoa landscape

“…Indigenous forest trees retained on the landscape can provide a number of benefits including improved nutrient cycling and increased biomass (Isaac et al 2007), reduced soil erosion, enhanced profitability and ecological resilience (Duguma et al 1998), and reduce pathogen and insect attack (Bos et al 2007). Overall, perceptions of trees as a biophysical component of the farm were surprisingly limited, and tended to focus rather narrowly on shade provision without acknowledging the myriad benefits to soil fertility, erosion control or integrated pest management.…”